Fatigue testing machine



April 1, 1952 B. J. LAzAN FATIGUE TESTING MACHINE 2 SHEETS- SHEET lFiled Oct. 22. 1946 |NVENTQR wff,

BENJAMIN d. LAZAN m G F02 m April 1, 1952 B. J. LAzAN FATIGUE TESTINGMACHINE 2 Sl-IEETS-SHEET 2 Filed OCT'. 22, 1946 1 M ICR@ :TCH

INVENTOR Patented Apr. 1., 1952 VFarmers TESTING MACHNE Benjamin J.Lazan, Syracuse, N. Y., assigner, by mesne assignments, toBaldwin-LirnaHamilton Corporation, a corporation of PennsylvaniaApplication October 22, 1946, Serial No. 704,814

(cl. 73u91) 6 Claims.

My invention relates generally to inertia comL pensated materialsfatigue testing machines of the below resonance type having an eccentricweight for producing an alternating centrifugal force to be applied to aspecimen.

One form of this general type of machine is shown in my co-pendingapplication, Serial No. 569,5l9,`filed December 23, 1944, now U. S.Patent 2,486,567,`but it is primarily adapted for pro ducing alternatingforces of considerably larger values than is desired in my presentinvention and therefore such prior machine has certain structuralcharacteristics that are necessary for producing and handling the largerforces and size of specimens therefor. These characteristics, whileessential for larger values of force, are not `conducive to the lowcost, minimum space and low force range which are desired in theinvention hereof.

It is an object of my present invention to provide an improved inertiacompensated fatigue testing machine of the below resonance type forforces of low magnitude and to provide such a'nmachine that is extremelysimple in construction. operation and maintenance and is compact, whileat Vthe same time maintaining a high degree of accuracy and sensitivity.

Other objects and advantages will be more apparent to those skilled inthe art from the following description of the accompanying drawings inwhich:

, Fig 1 is a longitudinal sectional View of my atigue testing machine;

` Fig. 2 is a transverse View of the fatigue machine along the line 2-2of Fig. l in the direcn tion of the arrows;

I Fig. 3 is a sectional plan view of the pillow blocks, along the line 33 of Fig. 2, showing the method by which a guide link is pivotallyattaohed therein;

. Fig. 4 is a sectional elevation of said pillow blocks and said guidelink, along the line ll-l of Fig. 1, showing the method of attaching theotheruend of said guide link to the rotating neigible shaft; y

Fig. 5 is an enlarged vertical sectional view `of the loading yoke,along the line 5--5 of Figi, inlthe direction of the arrows; and

` Fig. 6 diagrammatically illustrates a modified inertia compensatingshaft supported at each end so as to bend in the center.

In the particular embodiment of the inventionudisclolsed herein,Iwhaveshown my machine useimirnone specific. test, among Possible othersfor which it is adapted, consisting of a flexural test in which anelongated flat specimen I is held at one end by a stationary clampgenerally indicated at 2 and whose other end is held in a clamp 3 whichis reciprocated vertically to apply an alternating fatiguing force tothe specimen. To produce the alternating force and at the same timecompensate for inertiaeffects of the moving masses, all in a simple andaccurate manner, I provide an electric motor 3', Fig. -1, preferablysecured to the underside of the top of a housing Il by bolts 5. Ahorizontal shaft t constitutes in effect an appreciable extension of themotor shaft, and this shaft extension is preferably, but notnecessarily, separate from the motor shaft. This extension isspecifically obtained by having the inner vend of shaft 6 provided withan annular flange 1 which is cohnected to the motor shaft substantiallyco-axial ly therewith by a suitable collar `8 and bolts -9 that rigidlyhold said flange in contact with the motor shaft. This flange and collarconnection allows for whatever small amount of lateral adjustment may benecessary of shaft zi` with respect to the motor shaft in order'toobtain 'a balanced running condition of the shaft 6 by itself when noadditional elements are attached thereto. Secured to the end of theshaft-1s a centrifugal force producing eccentric weight IIl which isformed on a screw II threaded through a shaft hub I2. The radius of theweight, and therefore the centrifugal force produced thereby, isadjusted by rotating the'screw about its own axis to move the weight incrout. A thumb nut I3 locks the screw 4in any selected position.

As the weight revolves, its centrifugal force causes the shaft 6 to bendso that the shaft end would move in a circle except for the `use ofmeans, to be described later, which restrains the shaft in a lateraldirection only, thereby al lowing complete freedom of alternate bendingin a vertical plane. To transmit the centrifugal force tothe specimen,`Ipprovide'a rod I4 preferably threaded throughout its length Vconnectedto the shaft by a bearing I5. The 'upper end of rod I4 passes through aslot I6, running lengthwise of the machine in the top 'of housing 4 andis adjustably threaded into a specimen loading yoke I'I, Figs. 1, 2 'and5 of the movable clamp. Between the vertical arms of loading yoke I'I isa 'shaft I8, Figs. 2 and 5, journaled in suitable bearings I9, I9, thecentral portion of loading shaft I8 being recessed in thefrnanner `shown"Fig, 5 toaccinmodate one nd fthe normally horihtally dispbsd "spc riin`I` 'as shown in Fig. 1. A small plate 20, positioned directly abovesuch recessed portion of loading shaft I8, clamps said end of thespecimen in such recess by means of clamp screws 2|, 2| which passthrough holes in plate 20 and thread into loading shaft I8. Connectingrod I4 also passes loosely through two rubber rings 22, 22 secured tothe housing in the position shown in Fig. l for the purpose ofcushioning the blow of the descending loading yoke II and for cushioningthe upward movement of limit stop nuts 23, in the event a specimen failsand the load is thus substantially removed from connecting rod I4 or inthe event of excessive flexing of the specimen in case of improperadjustment of the centrifugal weight for a given size specimen.

The stationary clamp for the inner end of the specimen has a clampingblock 26, adjustably mounted on top of housing d over slot It. Insertedin a vertical hole in clamping block 2li and projecting downwardlythrough slot It is athreaded bolt 25 to the end oi' which a nut 25 isattached. When the clamping block has been adjusted along said Vslot tothe proper distance from loading' shaft I8, in order to receive theother end of the specimen, nut 26 is tightened on bolt 25, securingclamping bioek 2li rmly to the top of the housing. A pin 21, verticallyposi tioned through nut 26 and extending into slot I6, prevents nut 2Bfrom being turned by vibrap tion of the machine when in operation. Aplate 28 securely clamps the other end of the specimen in position bymeans of clamp screws 29, 2d which pass'through holes in said plate andthread into clamping block 2li, as shown in Fig. 2. Thus, p

whileV this end of the specimen is immovably held, the end of thespecimen clamped between shaft I8 and plate 2B is free to be verticallyvibrated through the motion of connecting rod I4 and loading yoke I'F,bringing about the desired iiexure of the specimen.

To restrain lateral movement of the shaft during rotation of theeccentric weight, a radius or guiding link 3G, Figs. 2, 3 and 4,preferably threaded throughout its length, has a bearing 3l at one endjournaled on the shaft 6 alongside of bearingl. The other end of theradius link 3l! passes through an enlarged opening 32 in the housing andthence through a horizontal rocker shaft 33 toV be secured thereto bynuts 34. The rocker shaft is disposed at right angles to link 3G and isjournaled in pillow blocks 35 secured to the housing by bolts 36. Link3i! is therefore capable ofV oscillation in a vertical plane about itscross shaft 33 as a center thereby restraining lateral movement of shaft6. Two weights 31 are threaded on guide link 30 for adjustment along itslength to maintain the vibrating parts at resonance when operated,without a specimen, with any given set of clamps or fixtures. Asexplained in my said cc-pending application a machine of this generaltype must be in resonance when operated with the additional weight ofthe iixtures, but without a specimen. If fixtures of different weightare substituted, then the weights 31 are adjusted accordingly, Theweight of whatever specimen to be used is of course also to be takeninto consideration. With the unloaded machine in resonance, it will,when a specimen is inserted, then operate 'below resonance due to theresistance of the bending force in the test specimen thereby resultingin an accurately known alternating source beingapplied to the specimen.The machine is preferably designed so that it is in resonance when theweights are adjusted fully inwardly close to shaft 6 with no xture orspecimen present. This allows for taking care of the largest range ofweights of fixtures and specimens in that the adjusted weights 31 can beadjusted outwardly for the full length of the radius link.

Inertia compensation of all reciprocating masses is obtained byutilizing the spring effect of the bending shaft The larger the masses,the stiffer the spring effect should be and hence the shaft may bestraight if desired or tapered as shown or instead of being a cantileverit may be a beam E supported'at one end by the motor as in Fig. 1 and atits outer end by a well known self aligning bearing diagrammaticallyindicated at 6". Fig. 6, the eccentric and other links being located atthe middle portion where bending would be the greatest. Thus it is seenthat the shaft of either type performs dual functions. one to carry androtate the eccentric weight I0 together with allowing bending toVtransmit the centrifugal force to the specimen, and, the other,

' to provide a spring action for counteracting the inertia effects ofthe moving masses and thereby prevent transmission of inertia forces tothe specimen. Hence by merely knowing the radius of the eccentric massiii, it is possible `to calculate with precision the true force thatwill be transmitted to the specimen. 'I he ability to combine the dualprinciples of operation in a single shaft is conducive to maximumsimplicity, compactness and economy of construction, operation andmaintenance7 A micro-switch 38, Figs. l and 2, is positioned .so thatits trigger lever 39 is located directly beneath the verticallyvibrating free end of guide link 30. When the specimen fails, the radiusguide link 3o strikes the trigger lever of the microswitch andautomatically turns off the electric motor 3. The obvious wiring circuitis omitted for clarity.

Connected to an extension of the motor shaft Y on the other side ofelectric motor 3', Fig. 1, is

a counter 4f) of any well known type which registers the number of timesa specimen is fiexed before failure occurs.

In operation-The specimen is clamped in position for flexing, as abovedescribed, and the electric motor rotates exible shaft 6 together witheccentric it which is attached thereto. The rotation of eccentric Hlproduces at the free end of iiexible shaft 6 a centrifugal force which,were it not for the presence of lateral guide link 30, would cause thefree end of iiexible shaft 6, while rotating, to describe a circle,carrying with ,it

through such circle rotating eccentric I0 and the lower end of verticalconnecting rod I4. VHowever, the presence of link 3U causes the lateralcomponent of said centrifugal force to be resisted and in effecteliminated, leaving evident only the vertical component thereof. Themotion of the free end of flexible shaft 6 is essentially andpractically vertical. This vertical component of said centrifugal force,produced by the rotationof eccentric I0. is transmitted through bearingI5, Fig. l, at the lower end of vertical rod I4, thence through thisconnecting rod to loading yoke I'I, Figs. 2 and 5, bearings I9, I9,loadingshaft I8 and thence to the end of specimen I, which is grippedbetween clamp shaft I8 and plate 20, causing the specimen, whose otherend is immovably held by clamping block 2, to be alternately exed with areversed bending load during each revolution of the motor shaft, i'lrstAin an upward direction and then in a downward direction. The mounting ofclamp shaft i8 in bear ings I9, i9, avoids any undesirable binding orstrain upon either end of the specimen, for when the movable end of thespecimen is forced upwardly or drawn downwardly by the vibratory actionof connecting rod I4 and loading yoke l1,

the shaft i8 freely rotates, one way or the other to accommodate itselfto the changing angle of said end of the specimen. When the specimenfinally fails, the vertical component of the centrifugal force, beingsuddenly freed of the restraint imposed by the specimen, causesconnecting rod I4 to vibrate through a greater distance. However, thefirst increased downward stroke of the end cf flexible shaft 6, causesbearing 3| at the inner end of radius link Sil to strike the triggerlever of the micro-switch, as shown in Fig. 2, which turns off theelectric motor and stops the machine.

From the disclosure herein, it is seen that I have provided a fatiguetesting machine in which the eccentric weight is supported on a flexibleshaft in a most unique manner so that its spring forcernay beeffectively utilized for resisting the inertia effects of thereciprocating masses. By the realization that both of these functionscan be obtained in a single rotating shaft, I am able to provide acompact low capacity and relatively inexpensive inertia compensatedfatigue testing machine without in any way sacrificing the precisionqualities necessary in an instrument of this type.

It will, of course, be `understood by those skilled in the art thatvarious changes may be made in the construction and arrangement of partsWithout departing from the spirit of the invention as set forth in theappended claims.

I claim:

l. fatigue testing machine comprising, in combination, a flexible driveshaft rotatable at a constant spoed and having eccentric means mountedthereon for rotation therewith to produce a centrifugal force andflexing said shaft, means for rigidly supporting one end of the shaft sothat the axis of said end remains in a single stationary position at alltimes, means for rotating said shaft, means for operatively connecting aspecimen to the flexing zone of said shaft at a fixed point remote fromsaid rigidly supported end so that the centrifugal force is applied tothe specimen upon fiexure of the shaft, means for guiding said remoteportion of the shaft so that said force produces substantially only areciprocating movement thereof, and said shaft having a spring constantsuch as to compensate for the inertia forces of all reciprocating massesconnected to the shaft, thereby to produce a load force in the specimenequal only to that of the centrifugal force.

2;- The combination set forth in claim 1 further characterized in thatthe guiding means has provision for restraining lateral bending of theshaft While allowing it to bend substantially only in a direction atright angles thereto for applying the force to the specimen, and themeans for operatively connecting the specimen to the shaft includes alink extending from the shaft in said right angle direction in which thecentrifugal forceis effective in inducing a loading force in thespecimen.

3. The combination set forth in claim 1 further characterized in thatthe guiding means includes a radius link connected at one end to saidshaft and means for supporting the other end of said link so thatbending of the shaft occurs in only one plane, and means mounted on saidlink to compensate for different weights of specimen connecting means.

el. The combination set forth in claim 1 further characterized in thatsaid shaft is a cantilever supported at its stationary end and whoseremote end is adapted to have movement in proportion to the centrifugalforce produced.

5. The combination set forth in claim 1 further characterized by theprovision of an electric motor having a shaft and the flexible shaftconstitutes a cantilever extension of the motor shaft to be supportedsolely thereby.

6. The combination set forth in claim 1 further characterized in thatthe exible shaft is a tapered cantilever.

BENJAMIN J. LAZAN.

No references cited.

